Photoelectrophoretic imaging process employing quinacridone pigments

ABSTRACT

A novel composition having the formula:   WHEREIN R CH3, C2H5, OCH3, OC2H5 or a halogen and wherein R&#39;&#39; an aromatic, heterocyclic, alicyclic or aliphatic group is disclosed. Methods of preparing said composition and of using said composition in electrophoretic imaging processes are also disclosed.

United States Patent [191 Weinberger Aug. 21, 1973 1 [75] Inventor:

[ 1 PHOTOELECTROPHORETIC IMAGING PROCESS EMPLOYING QUINACRIDONE PIGMENTS Related US. Application Data [60] Division of Ser. No. 129,078, March 29, 1971, Pat. No. 3,705,901, Continuation-impart of Ser. No. 754,634, Aug. 22, 1968, abandoned.

3,418,322 12/1968 Fulagin ..260/279R 3,473,940 10/1969 Walsh .260/279R Primary Examiner-Norman G. Torchin Assistant Examiner-John R. Miller Attorney-James J. Ralabate et a1.

[57] ABSTRACT A novel composition having the formula:

wherein R =CH C 11 OCH OC H or a halogen and wherein R' an aromatic, heterocyclic, alicyclic or aliphatic group is disclosed. Methods of preparing said composition and of using said composition in electrophoretic imaging processes are also disclosed.

8 Claims, 1 Drawing Figure [52] US. Cl 96/1 PC, 96/l.2,96/1.3, 96/l.5, 204/181 PE [51] Int. Cl. G03g 13/00, 603g 5/00 [58] Field of Search 96/1 PC, 1.2, 1.3; 204/181 PE; 260/279 R [56] References Cited UNITED STATES PATENTS 3,635,981 l/l972 Weinberger 260/279 R 3,275,637 9/1966 West 260/279 R PHOTOELECTROPHORETIC IMAGING PROCESS EMPLOYING QUINACRIDONE PIGMENTS This application is a division of copending application Ser. No. 129,078, filed Mar. 29, 1971, now US. Pat. No. 3,705,901, which is a continuation-in-part of application Ser. No. 754,634, filed Aug. 22, 1968, now abandoned.

BACKGROUND OF THE INVENTION This invention relates, in general, to novel quinacridone pigments and to methods of preparing same, as well as to the use of said pigments in photoelectrophoretic imaging systems.

There has been recently developed an electrophoretic imaging system capable of producing color images which utilizes single-component photoconductive particles. This process is described in detail and claimed in O l g US. Pat. Nos. 3,384,565, 3,384,566 and 3,385,488. In such an imaging system, variously colored light absorbing particles are suspended in a non-conductive liquid carrier. The suspension is placed between electrodes, subjected to a potential difference and exposed to an image. As these steps are completed, selective particle migration takes place in image configuration, providing a visible image at one or both of the electrodes. An essential component of the system is the suspended particles which must be electrically photosensitive and which apparently undergo a net change in charge polarity upon exposure to activating electromagnetic radiation, through interaction with one of the electrodes. In a monochromatic system, particles of a single color are used; producing a single colored image equivalent to conventional black-and-white photography. In a polychromatie system, the images are produced in natural color because mixtures of particles of two or more different colors which are each sensitive to light of a specific wavelength or narrow range of wavelengths are used. Particles used in this system must have both intense pure colors and be highly photosensitive. The pigments of the prior art often lack the purity and brilliance of color, the high degree of photosensitivity, and/or the preferred correlation between the peak spectral response and peak photosensitivity necessary for use in such a system.

Still another object of this invention is to provide photoelectrophoretic imaging processes capable of producing color images.

Yet another object of this invention is to provide photoelectrophoretic imaging processes utilizing particles having photographic speed and color qualities superior to those of known pigments.

Still another object of this invention is to provide novel compositions for use in the pigment trade as well as in various imaging processes.

Another object of this invention is to provide methods for the preparation of novel pigment compositions.

SUMMARY OF THE INVENTION The foregoing objects, and others, are accomplished in accordance with this invention, generally speaking, by providing a novel class of quinacridone pigments having the general formula:

wherein R=CH C ll OCH OC H or a halogen and R an aromatic, heterocyclic, alicyclic or aliphatic group and, further, by providing a method for the preparation of said class of pigments as well as by providing photoelectrophoretic imaging processes utilizing this novel class of pigments. This novel class of pigments It is, therefore, an object of this invention to provide photoelectrophoretic imaging processes utilizing photosensitive pigment particles which overcome the above-noted deficiencies.

Another object of this invention is to provide highly photosensitive particles for use in electrophoretic imaging systems.

has been found to have electrically photosensitive or photomigratory characteristics such as to make them especially useful in photoelectrophoretic imaging systems.

While any of the novel class of quinacridones having the above-described general formula may be used in photoelectrophoretic imaging systems, it is preferred to employ those quinacridones wherein R is selected from the group consisting of CH C,ll-I and mixtures thereof and wherein R since these materials have especially pure color and are highly photosensitive for use in electrophoretic imaging processes. The quinacridone pigments of the present invention may have other compositions added thereto to sensitize, enhance, synergize or otherwise modify its properties.

The novel class of quinacridone pigments of thisinvention may be prepared by any suitable method. A preferred method of preparing said quinacridone pigments, wherein large yields of a substantially pure final product are obtained, comprises first mixing a compound with the general formula:

where R CH C H OCH OC,H or a halogen, in SOCl and dimethyl formamide; then mixing the resulting compound with 2R'NH where R =.an aromatic,

3 heterocyclic, alicyclic, or aliphatic group; heating the mixture to reflux and pouring the mixture over ice.

The use of pigments comprising the novel class of quinacridones of the present invention in photoelectrophoretic imaging processes may be further understood by reference to the FIGURE which shows an exemplary electrophoretic imaging system.

Referring now to the FIGURE, there is seen a transparent electrode generally designated 1 which, in this exemplary instance, is made up of a layer of optically transparent glass 2 overcoated with a thin optically transparent layer 3 of tin oxide, commercially available under the name NESA glass. This electrode will hereafter be referred to as the injecting" electrode. Coated on the surface of injecting electrode 1 is a thin layer 4 of finely divided photosensitive particles dispersed in an insulating liquid carrier. The term photosensitive, for the purposes of this application, refers to the properties of a particle which, once attracted to the injecting electrode, will migrate away from it under the influence of an applied electric field when it is exposed to actinic electromagnetic radiation. For a detailed theoretical explanation of the apparent mechanism of operation of the invention, see the above-mentioned US. Pat. Nos. 3,384,565; 3,384,566 and 3,385,488, the disclosures of which are incorporated herein by reference. Liquid suspension 4 may also contain a sensitizer and- /or a binder for the pigment particles which is at least partially soluble in the suspending or carrier liquid as will be explained in greater detail below. Adjacent to the liquid suspension'4 is a second electrode 5, hereinafter called the blocking electrode, which is connected to one side of the potential source 6 through a switch 7. The opposite side of potential source 6 is connected to the injecting electrode 1 so that when switch 7 is closed, an electric field is applied across the liquid suspension 4 between electrodes 1 and 5. An image projector made up of a light source 8, a transparency 9, and a lens 10 is provided to expose the dispersion 4 to a light image of the original transparency 9 to be reproduced. Electrode 5 is made in the form of a roller having a conductive central core 11 connected to the potential source 6. The core is covered with a layer of a blocking electrode material 12, which may be Baryta paper. The pigment suspension is exposed to the image to be reproduced while a potential is applied across the blocking and injection electrodes by closing switch 7. Roller 5 is caused to roll across the top surface of injecting electrode 1 with switch 7 closed during the period of image exposure. This light exposure causes exposed pigment particles originally attracted to electrode l to migrate through the liquid and adhere to the surface of the blocking electrode, leaving behind a pigment image on the injecting electrode surface which is a duplicate of the original transparency 9. After exposure, the relatively volatile carrier liquid evaporates off, leaving behind the pigment image. This pigment image may then be fixed in place as, for example, by placing a lamination over its top surface or by virtue of a dissolved binder material in the carrier liquid such as paraffin wax or other suitable binder that comes out of solution as the carrier liquid evaporates. About 3 to 6 percent by weight of paraffin binder in the carrier has been found to produce good results. The carrier liquid itself may be liquified paraffin wax or other suitable binder. In the alternative, the pigment image remaining on the injecting electrode may be transferred to another surface and fixed thereon. As explained in greater detail below, this system can produce either monochromatic or polychromatic images depending upon the type and number of pigments suspended in the carrier liquid and the color of light to which this suspension is exposed in the process.

Any suitable insulating liquid may be used as the carrier for the pigment particles in the system. Typical carrier liquids are decane, dodecane, N-tetradecane, paraffin, beeswax or other thermoplastic materials, Sohio Odorless Solvent 3440, (a kerosene fraction available from Standard Oil Company of Ohio), and lsopar-G, (a long chain saturated aliphatic hydrocarbon available from Humble Oil Company of New Jersey). Good quality images have been produced with voltages ranging from 300 to 5,000 volts in the apparatus of the figure.

In a monochromatic system, particles of a single composition are dispersed in the carrier liquid and exposed to a black-and-white image. A single color results, corresponding to conventional black-and-white photography. In a polychromatic system, the particles are selected so that those of different colors respond to different wavelengths in the visible spectrum corresponding to their principal absorption bands. Also, the pigments should be selected so that their spectral response curves do not have substantial overlap, thus allowing for color separation and subtractive multicolor image formation. In a typical multicolor system, the particle dispersion should include cyan colored particles sensitive mainly to red light, magenta particles sensitive mainly to green light and yellow colored particles sensitive mainly to blue light. When mixed together in a carrier liquid, these particles produce a black appearing liquid. When one or more of the particles are caused to migrate from base electrode 11 toward an upper electrode, they leave behind particles which produce a color equivalent to the color of the impinging light. Thus, for example, red light exposure causes the cyan colored pigment to migrate, leaving behind the magenta and yellow pigments which combine to produce red in the final image. lnthe same manner, blue and green colors are reproduced by removal of yellow and magenta, respectively. When white light impinges upon the mix, all pigments migrate, leaving behindthe color of the white or transparent substrate. No exposure leaves behind all pigments which combine to produce a black image. This is anideal technique of sub- It has been found that the novel class of quinacridones as discussed above are surprisingly effective when used in either a single or multicolor electrophoretic imaging system. Their good spectral response and high photosensitivity result in dense, brilliant images.

Any suitable different colored photosensitive pigment particles having the desired spectral responses may be used with the novel magenta quinacridone pigments of this invention to form a partial suspension in a carrier liquid for color imaging. From about 2 to about 10 percent pigment by weight have been found to produce good results. The addition of small amounts (generally ranging from 0.5 to 5 mol percent) of electron donors or acceptors to the suspensions may impart significant increases in system photosensitivity.

The following examples further specifically define 6 the present invention with respect to the use of the ball mill for 48 hours to reduce their size to provide a compositions of the general formula given above in more stable dispersion which improves the resolution electrophoretic imaging processes. Parts and percentof the final images. The exposure is made with a ages are by weight unless otherwise indicated. The ex- 3,200K. lamp through a 0.30 neutral density step amples below are intended to illustrate various pre- 5. wedge filter to measure the sensitivity of the suspenferred embodiments of the electrophoretic imaging sions to white light and then Wratten filters 29, 61 and process of the present invention. 47b are individually superimposed over the light source in separate tests to measure the sensitivity of the sus- DESCRIPTION OF THE PREFERRED pensions to red, green and blue light respectively.

EMBODIMENTS 10 The following examples are carried out in an appara- EXAMPLE I tus of the general type illustrated in the figure with the About 100 ml. of dimethylformamide are placed in imaging mix 4 coated on a NESA glass substrate a 500 ml. glass flask fitted with a reflux column and through which exposure is made. The NESA glass surdrying tube containing CaCl,. Approximately 14.0 g. of face is connected in series with a switch, a potential IS a compound having the formula:

A r. r 0 CH CHzNH-@ g 0 I NHCNT- on. cozrr N H ll 01H 0 source, and the conductive center of a roller having a are then suspended in the dimethylformamide. About coating of Baryta paper on its surface. The roller is ap- 3.2 ml. of SOCl are then added to the suspension. At proximately 2% inches in diameter and is moved across this point there is an evolution of heat. About 4.2 g. of the plate surface at about 1.45 centimeters per second. NH, in about 20 ml. of dimethylformamide are then The plate employed is roughly3 inches square and is added to the solution and the mixture is refluxed for exposed with a light intensity of 8,000 foot candles as about 1 hour. After refluxing, the solution is poured measured on the uncoated NESA glass surface. Unless over ice and filtered. There resulting material appears otherwise indicated, 7 percent by weight of the indimagenta in color and has the formula:

T 0 ll cari C) NHCH ii iu cated pigments in each example are suspended in Sohio EXAMPLES Il VI Odorless Solvent 3440 and the magnitude of the ap- The procedure of Example l is repeated sing about plied potential is 2,500 f p i which have 0.02 moles of the following starting materials in place a relatively large particle size as made are ground in a f; y

in Example III 0 ll g (I) 011m cnmm l- Q 0 Cj -limr0hr O 0 V 0 -0c21'n 0211 w H ll (10,11 0

in Example IV O NI-ICHa- -Cl l 02H in Example VI In each instance (Examples ll Vl) there resulted resulting pigments were found to have the following magenta-colored pigments. Upon chemical analysis the formulas:

in Example II II p 0 (111.0 CH,NH 0 ll CNHCH, \N/ OCH; 0 n u 0 C-NH m NH-fi l0 0/ in Example III 0 g I c,H,o @lCH,NHC G I -ONHCH, OCZHJ 2% H g C-NH NH 0 I I I N in Example IV \-CH;NHC'/ in Example V EXAMPLES Vll Vlll materials, as listed above, may be used with similar results. In addition, other materials may be added to the pigment compositions to synergize, enhance, or otherwise modify their properties. The novel pigment compositions of this invention may be dye sensitized, if desired, or may be mixed with other photosensitive materials, both organic and inorganic.

It will be appreciated by those skilled in the art upon a reading of the present disclosure that other modifica tions and ramifications are possible which are within the spirit of the invention and the scope of the claims.

What is claimed is:

l. A method of electrophoretic imaging comprising subjecting a layer of a suspension to an applied electric field between at least two electrodes, at least one of which is partially transparent, and simultaneously exin Example VI About 4 parts of the novel magenta quinacridone pigment of Example I are suspended in about 100 parts of Sohio Odorless Solvent 3400, a kerosene fraction available from Standard Oil of Ohio. In Example Vll the mixture is coated on the NESA glass substrate and a negative potential is imposed on the roller electrode. Four exposure tests are made through the neutral density step wedge filters and color filters as indicated above, to test the suspension for sensitivity to red, green, blue and white light. In Example VIll, the steps are repeated with the lower electrode at a positive potential. These novel magenta pigments are found to be primarily sensitive to green light with white light sensitivity being substantially the same as the green light sensitivity.

posing said suspension to an Image through said trans- EXAMPLES IX and X parent electrode with activating electromagnetic radia- The pigment prepared in Example 11 is suspended tion whel:eby a Pigment image made P of migrated and tested as in Examples VII and VIII above. Results paftlcles formed f least elwfqdes; indicate that this novel quinacridone magenta pigment sa'd suspenslon compnsmg a pluralfty of finely dmded has excellent photographic speed and excellent density Paltlcles of at least one color pamcles f one characteristics color comprising a quinacridone having the formula:

O R /N\ 431191118- l @("JNHGH O c C) R 0 i N H H RNH-C o 7 c-NH-R' EXAMPLES XL and Xll wherein R is selected from the group consisting of CH The pigment of Example lll is suspended. and tested z s, a, z s a halogenrand mixtures there) as in Examples VII and Vll]. This pigment demonand wherein R is a pyrydyl group. a strates good photographic speed and produces an 2. The method of claim lwherein R is selected from image of good density. tEe grfoup consisting of CH;,, C I-l, and mixtures t ereo I EXAMPLES xm and XIV 3. The method of claim 1 wherein at least one of said The pigment of Example V is suspended and treated electrodes is a blocking electrode. as in Examples Vll and VIII. This novel pigme is 4. The method of claim 3 wherein R is selected from found to have good photographic speed to produce he ou consisting of CH C,H and mixtures good images with either a negative or positive potential th f, on the roller electrode. 5. A method of electrophoretic: imaging comprising As shown by the above examples the no Class Of subjecting a layer of a suspension to an applied electric qulnacrldlmesi 0f the Present invention, in g arc field between two electrodes, at least one of which is at suitable for use in electrophoretic imaging processes. least artl transparent, said suspension comprising a Smce their photographic speed, density characteristics |i offinely divid d particles of at least two differand color characteristics vary, a mixture of the particuent colors in an insulating carrier liquid, the particles lar pigments may be preferred for specific uses. Some of each color comprising a photosensitive pigment characteristics of the pigments may be improved by whose principal light absorption band substantially coparticular purification processes, recrystallization proincides with its principal photosensitive response, sicesses and dye sensitization. multaneously exposing said suspension to a light image Although specific components and proportions have through said partially transparent electrode and then been described in the above examples, other suitable separating said electrodes whereby a migrated pigment image is formed on the surface of at least one of said the group consisting of CH C l-l and mixtures electrodes, the particles of one color comprising a thereof. quinacridone having the formula: 7. The method of claim 5 wherein at least one of said CNHR wherein R is selected from the group consisting of CH electrodes is a blocking electrode. C,H OCl-l OC H a halogen, and mixtures thereof 8. The method of claim 7 wherein R is selected from and wherein R is a pyrydyl group. the group consisting of CH C H and mixtures 6. The method of claim 5 wherein R is selected from thereof. 

2. The method of claim 1 wherein R is selected from the group consisting of CH3, C2H5 and mixtureS thereof.
 3. The method of claim 1 wherein at least one of said electrodes is a blocking electrode.
 4. The method of claim 3 wherein R is selected from the group consisting of CH3, C2H5 and mixtures thereof.
 5. A method of electrophoretic imaging comprising subjecting a layer of a suspension to an applied electric field between two electrodes, at least one of which is at least partly transparent, said suspension comprising a plurality of finely divided particles of at least two different colors in an insulating carrier liquid, the particles of each color comprising a photosensitive pigment whose principal light absorption band substantially coincides with its principal photosensitive response, simultaneously exposing said suspension to a light image through said partially transparent electrode and then separating said electrodes whereby a migrated pigment image is formed on the surface of at least one of said electrodes, the particles of one color comprising a quinacridone having the formula:
 6. The method of claim 5 wherein R is selected from the group consisting of CH3, C2H5 and mixtures thereof.
 7. The method of claim 5 wherein at least one of said electrodes is a blocking electrode.
 8. The method of claim 7 wherein R is selected from the group consisting of CH3, C2H5 and mixtures thereof. 